The present disclosure relates generally to material handling systems, and is more particularly directed to gapping methods and systems that provide a desired gap between articles (e.g., cartons) within a continuously flowing train of articles.
Establishing a correct gap between cartons within a continuously flowing train of cartons has become an increasingly difficult problem to solve over the last several decades. At low speeds, there is no real challenge. For example, if two cartons, traveling at 100 feet per minute (FPM) have only 1 inch of gap between them, but require 12 inches, the control system can easily create the required gap, because (at 0.5 g) the second carton can be stopped within an inch of travel after the previous carton has exited the conveyor. However, as the speed of the cartons increases, the conveyor takes longer to stop (at the same deceleration rate). Also, the carton is traveling at a higher average speed during that extended time. Hence, the distance required to stop a carton increases with the square of the increase in speed.
As a result, at 600 FPM, the travel distance which the second carton requires in order to increase the gap between itself and the previous carton (constantly moving at 600 FPM) by 11 inches is 46 inches. Obviously, there is not nearly enough space available to effect this change after the first carton exits the controlling conveyor.
Conventional single-stage gapping units must either give up or release at a speed which will usually cause the required gap to be “pulled” between the cartons. This method, while it can be reasonably effective with exotic algorithms applied, is based on assumed weight transfer points for cartons and inadvertently effects gapping of neighboring cartons. The result, unavoidably, is a level of ineffectiveness that worsens at higher speeds.